Transcript Effects of Climate Change on Snowpack, Runoff, Soil Moisture and

Effects of Climate Change on
Snowpack, Runoff, Soil Moisture and
Evaporation in the Western U.S. from
1916-2003
Center for Science in the Earth System
Climate Impacts Group
and Department of Civil and Environmental Engineering
University of Washington
September, 2005
Alan F. Hamlet,
Phil Mote, Martyn Clark,
Dennis P. Lettenmaier
Background
Winter Climate of the Western U.S.
PNW
GB
CA CRB
DJF Temp (°C)
NDJFM Precip (mm)
Long Term Water Balance Simulation for the Colorado River Basin
80
60
precipitation
50
swe
40
runoff+baseflow
soil storage
30
evapotranspiration
20
10
sep
aug
jul
jun
may
apr
mar
feb
jan
dec
nov
0
oct
Area Average Water
(depth in mm)
70
Natural AND human influences explain the observations of
global warming best.
Natural Climate Influence
Human Climate Influence
All Climate Influences
Changes in Simulated April 1 Snowpack for
the Cascade Range in Washington and
Oregon for Middle-of-the-Road Climate
Change Scenarios
Current Climate
“2020s” (+1.7 C)
-44%
April 1 SWE (mm)
“2040s” (+ 2.25 C)
-58%
Effects to the Cedar River (Seattle Water Supply)
for “Middle-of-the-Road” Scenarios
9000
8000
+1.7 C
6000
Simulated 20th
Century Climate
2020s Climate
Change Scenario
2040s Climate
Change Scenario
5000
4000
3000
2000
+2.25 C
1000
Date
9/2
8/5
7/8
6/10
5/13
4/15
3/18
2/18
1/21
12/24
11/26
10/29
0
10/1
Inflow (acre-ft)
7000
600
Area Average Water
(depth in mm)
Seasonal
Water Balance
Naches River
700
500
precipitation
400
swe
runoff+baseflow
soil storage
300
evapotranspiration
200
100
Current Climate
sep
aug
jul
jun
may
apr
mar
feb
jan
dec
600
500
precipitation
400
swe
runoff+baseflow
soil storage
300
evapotranspiration
200
100
sep
aug
jul
jun
may
apr
mar
feb
jan
dec
nov
0
oct
2040s Scenario
(+ 2.25 C)
700
Area Average Water
(depth in mm)
More runoff in
winter and
early spring,
less in
summer
nov
oct
0
Trends in Temperature
and Precipitation
Trends in Winter (Oct-Mar) Precipitation and Temperature
DJF Avg Temperature
Precipitation
Tmin
Trend (°C/yr)
Trend (°C/yr)
Trend (°C/yr)
Trend (°C/yr)
19162003
Rel. Trend %/yr
DJF Avg Temperature
Tmax
19472003
Rel. Trend %/yr
Trends in Summer (Apr-Sept) Precipitation and Temperature
DJF Avg Temperature
Precipitation
Tmin
Trend (°C/yr)
Trend (°C/yr)
Trend (°C/yr)
Trend (°C/yr)
19162003
Rel. Trend %/yr
DJF Avg Temperature
Tmax
19472003
Rel. Trend %/yr
In temperature sensitive areas of the
West, we should be able to see the
effects of observed global warming in
the historic snow and streamflow
records.
Using models we should be able to
more fully analyze these changes, as
well as other hydrologic effects which
are not typically measured (evaporation
and soil moisture).
Schematic of VIC Hydrologic Model and Energy Balance Snow Model
PNW
GB
CA
CR
B
Snow Model
Trends in April 1 Snowpack
Trends in April 1 SWE 1950-1997
Mote P.W.,Hamlet A.F., Clark M.P., Lettenmaier D.P., 2005, Declining
mountain snowpack in western North America, BAMS (in press)
DJF avg T (C)
Overall Trends in April 1 SWE from 1947-2003
Trend %/yr
Trend %/yr
DJF avg T (C)
Temperature Related Trends in April 1 SWE from 1947-2003
Trend %/yr
Trend %/yr
DJF avg T (C)
Precipitation Related Trends in April 1 SWE from 1947-2003
Trend %/yr
Trend %/yr
Trends in April 1 SWE for the WA and OR Cascades
600
-19%
500
400
Effects of Temperature
And Precipitation
1-Apr
300
Linear (1-Apr)
200
-2.15% per decade
100
y = -0.5851x + 295.29
2001
1996
1991
1986
1981
1976
1971
1966
1961
1956
1951
1946
1941
1936
1931
1926
1921
1916
0
500
-25%
450
400
350
300
Effects of Temperature
Alone
1-Apr
250
Linear (1-Apr)
200
150
100
50
2001
1996
1991
1986
1981
1976
1971
1966
1961
1956
1951
1946
1941
1936
1931
1926
1921
0
1916
-2.84% per decade
y = -0.7553x + 301.86
Trends in April 1 SWE for the WA and OR Cascades
600
-35%
500
400
Effects of Temperature
And Precipitation
1-Apr
Linear (1-Apr)
300
200
-6.48% per decade
100
y = -1.739x + 313.96
2001
1998
1995
1992
1989
1986
1983
1980
1977
1974
1971
1968
1965
1962
1959
1956
1953
1950
0
400
-23%
350
300
250
Effects of Temperature
Alone
1-Apr
Linear (1-Apr)
200
150
y = -1.1264x + 288.63
100
50
2001
1998
1995
1992
1989
1986
1983
1980
1977
1974
1971
1968
1965
1962
1959
1956
1953
0
1950
-4.25% per decade
Obs. Summer Water Availability is Declining
0.7
Cedar River: -30.7%
May-Sept frac
Linear (May-Sept
frac)
0.5
0.4
0.3
0.2
0.6
SFTolt River: -15.7%
May-Sept frac
y = -0.0020x + 4.3416
0.1
0
1945
1955
1965
1975
55 years
1985
1995
2005
May-Sept fraction of annual flow
May-Sept fraction of annual flow
0.6
Linear (May-Sept
frac)
0.5
0.4
0.3
0.2
y = -0.0010x + 2.2890
0.1
0
1945
1955
1965
1975
1985
1995
Figures courtesy of Matt Wiley and Richard Palmer at CEE, UW
2005
Trends in timing of
peak snowpack are
towards earlier
calendar dates
Change in Date
a) 10 % Accumulation
b) Max Accumulation
c) 90 % Melt
Trends
in
SWE
19161997
Change in Date
Change in Date
Change in Date
DJF Temp (C)
DJF Temp (C)
DJF Temp (C)
Change in Date
Change in Date
Change in Date
Trends in Runoff Timing
As the West warms,
winter flows rise
and summer flows
drop
Stewart IT, Cayan DR,
Dettinger MD, 2004,
Changes toward earlier
streamflow timing across
western North America, J.
Climate (in review)
Trends in simulated fraction of annual runoff in each month
from 1947-2003 (cells > 50 mm of SWE on April 1)
March
Relative Trend (% per year)
June
Trends in June Runoff
DJF Temp (°C)
DJF Temp (°C)
Trends in March Runoff
Trend %/yr
Trend %/yr
Trends in Soil Moisture
April 1
DJF Temp (°C)
Trends in Simulated Soil Moisture from 1947-2003
July 1
DJF Temp (°C)
Trend %/yr
Trend %/yr
Trends in July 1 SM
DJF Temp (°C)
DJF Temp (°C)
Trends in April 1 SM
Trend %/yr
Trend %/yr
Trends in the “Runoff Ratio”
(runoff/precipitation)
Trend Runoff Ratio
Trend Runoff Ratio
DJF Temp (°C)
Trend Oct-Mar PCP
Trend %/yr
Trend Apr-Sep PCP
Conclusions
•Large-scale changes in the seasonal dynamics of snow
accumulation and melt have occurred in the West as a result of
increasing temperatures.
•Hydrologic changes include earlier and reduced peak snowpack,
more runoff in March, less runoff in June, and corresponding
increases in simulated spring soil moisture and decreases in late
summer and fall soil moisture.
•Because these effects are shown to be predominantly due to
temperature changes, we expect that they will both continue and
increase in intensity as global warming progresses in the 21st
century.
•Trends in the runoff ratio are primarily linked to winter
precipitation trends, which are not necessarily related to global
warming
Trends in Potential Evaporation
Average July PotET over the Southern Plain Region in the Snake River Basin
Current Climate vs. MPI2040 scenario
(Effects of temperature increases alone)
Current Climate
PotET (mm/day)
MPI2040
+4C
Trends in July Avg PotET over the Southern Plain Region from 1915-2002
8.5
7.5
7
jul
Linear (jul)
6.5
6
y = -0.0061x + 7.3589
5.5
2000
1995
1990
1985
1980
1975
1970
1965
1960
1955
1950
1945
1940
1935
1930
1925
1920
5
1915
Reference Crop PotET (mm/day)
8
Will Global Warming be “Warm and
Wet” or “Warm and Dry”?
Answer:
Probably BOTH!
450000
350000
300000
250000
200000
2000
1990
1980
1970
1960
1950
1940
1930
1920
1910
150000
1900
Apr-Sept Flow (cfs)
400000
Implications for Water Planning
•Water resources managers and planners should expect systematically
decreasing natural flows in summer in river basins with substantial winter
snow accumulation.
•Hydrologic changes due to global warming are likely to exacerbate future
stresses on water systems due to increasing population, and may intensify
existing conflicts between water supply and other objectives such as
instream flow for fish.
•There is little evidence in the historic record for systematic changes in
winter precipitation associated with global warming in the West. Water
managers should be prepared to cope with extended periods of both
“warm and wet” and “warm and dry” conditions at different times in the
future.
•Effects to potential evaporation (irrigation demand) remain unclear and
appear to be strongly affected by uncertain changes in cloudiness and
humidity in addition to temperature.
•Straight-forward methods to include these kinds of hydrologic changes in
water planning studies are readily available.
Selected References:
Hidalgo HG, Cayan DR, Dettinger MD, 2005: Sources of variability of
evapotranspiration in California, J. of 6 (1): 3-19
Hamlet A.F., Lettenmaier D.P., 2005, Production of temporally consistent gridded
precipitation and temperature fields for the continental U.S., J. of
Hydrometeorology, 6(3), 330-336
Hamlet A.F., Mote P.W, Clark M.P., Lettenmaier D.P., 2005, Effects of temperature
and precipitation variability on snowpack trends in the western U.S., J. of Climate
(in press)
Hamlet A.F., Mote P.W., Clark M.P., Lettenmaier D.P., 2005: 20th Century Trends in
Runoff, Evapotranspiration, and Soil Moisture in the Western U.S. , J. of Climate (in
review)
Mote P.W., Hamlet A.F., Clark M.P., Lettenmaier D.P., 2005, Declining mountain
snowpack in western North America, BAMS, 86 (1), 39-49
Stewart IT, Cayan DR, Dettinger MD, 2005: Changes toward earlier streamflow
timing across western North America, J. Climate, 18 (8): 1136-1155